A goal of the Third Generation Partnership Project (3GPP) Long Term Evolution (LTE) program is to develop new technology, new architecture and new methods for settings and configurations in wireless communication systems in order to improve spectral efficiency, reduce latency and better utilize the radio resource to bring faster user experiences and richer applications and services to users with lower costs.
Wireless communication systems usually require feedback signaling to enable uplink and downlink communications. For example, hybrid automatic retransmission request (HARQ) enablement requires acknowledge/non-acknowledge (ACK/NACK) feedback. Adaptive modulation and coding (AMC) requires channel quality index (CQI) feedback from a receiver. Multiple Input/Multiple Output (MIMO) systems or precoding requires rank and/or precoding matrix Index (PMI) feedback from a receiver. Typically, this type of feedback signaling is protected by coding and the signaling does not have error checking or detection capabilities. However, efficient signaling is essential to an evolved universal mobile telephone system (UMTS) terrestrial radio access network (E-UTRAN). Adding error check (EC) and error detection capability to the feedback control signaling makes more advanced applications possible. Error check (EC) and error detection capability can enable advanced signaling schemes, enhanced MIMO link performance, reduced system overhead, and increased system capacity.
An example of an application that may require error detection and checking capability for feedback control signaling is the preceding information validation. The precoding information validation is used to inform a WTRU about the precoding information that is used at an e Node B so that the effective channel seen by the WTRU that contains precoding effects can be reconstructed by the WTRU. This is required for accurate data detection for MIMO systems using precoding, beamforming or the like.
A wireless transmit receive unit (WTRU) may feedback a precoding matrix index (PMI) or antenna weight to a base station (BS) or an e Node B (eNB). To inform a WTRU of the precoding matrices used at an eNB, the eNB may send a validation message to the WTRU. Each matrix that the WTRU signals as feedback to the eNB may be denoted by PMI_j1, PMI_j2 . . . PMI_jN, where N is a integer value equal to the total number of matrices. The eNB may send a validation message containing information about N PMIs denoted by PMI_k1, PMI_k2 . . . PMI_kN to the WTRU.
Each PMI may be represented by L bits. The value of L depends upon the multiple input/multiple output (MIMO) antenna configuration and codebook sizes.
Communication resources may be assigned to a WTRU. A resource block (RB) consists of M subcarriers, for example M=12, where M is a positive integer. A resource block group (RBG) or sub-band may include N_RB RBs, where N_RB may equal, for example, 2, 4, 5, 6, 10, 25 or larger. A system bandwidth can have one or more RBGs or sub-bands depending on the size of bandwidth and value of N_RB per RBG or sub-band.
A WTRU may feed back one PMI for each RBG or sub-band that is configured to it. The terms RBG and sub-band may be used interchangeably. N RBGs, where N≦N_RBG, can be configured to or selected by a WTRU for feedback and reporting purpose. If N RBGs or sub-bands are configured to or selected by a WTRU, then the WTRU feeds back N PMIs to the eNB. The eNB may send the validation message consisting of N PMIs back to the WTRU.
Let N_PMI be a number of bits that represents a PMI. The total number of bits for the WTRU PMI feedback is N×N_PMI. The maximum number of bits for WTRU PMI feedback is N_RBG×N_PMI bits per feedback instance. When a straightforward precoding validation scheme is used, the maximum number of bits for PMI validation message is N_RBG×N_PMI bits per validation message.
Table 1 shows a number of bits for WTRU PMI feedback and signaling with the assumption that N_PMI=5 bits. The numbers are summarized for 5, 10 and 20 MHz bandwidth. The second row, N_RB, is the number of RBs per RBG or sub-band, which is in a range of 2 to 100 for 20 MHz. The third row, N_RBG per band, is the number of RBGs or sub-bands per 5, 10 or 20 MHz. The value of N_RBG is in a range from one to fifty. The fourth row is the total number of bits used for WTRU PMI feedback signaling per feedback instance. This is for frequency selective precoding feedback or multiple PMI feedback
TABLE 1Maximum number of bits for PMI feedback and PMI validation5 MHz10 MHz20 MHz(300 subcarriers)(600 subcarriers)(1200 subcarriers)N_RB per2510252510255025102550100RBGN_RBG135312510521502010421per bandMax # of652515512550251052501005020105bits forPMIfeedbackperfeedbackMax # of652515512550251052501005020105bits forPMIsignalingpermessageAssume 12 subcarriers per RB.N_RB: Number of resource blocks.N_RBG: Number of frequency RB groups.N_PMI: Number of bits to represent a PMI.Max number of bits for WTRU PMI feedback = N_RBG × N_PMI bits.Max number of bits for eNB validation message = N_RBG × N_PMI bits.
PMI feedback and PMI validation may require over 250 bits per feedback instance and per validation message as shown in the above table.
Feedback error significantly degrades the link and system performance. It would be desirable for feedback bits to be protected with error checking (e.g., channel coding). Furthermore, knowing whether there is an error in a feedback signal improves system performance such as link performance, because the erroneous feedback information can be avoided. Furthermore, knowing whether there is error in the feedback signaling enables the use of advanced signaling schemes or applications such as the precoding confirmation and indication schemes. Precoding confirmation can be sent to confirm the correctness of feedback signaling if there is no error in the feedback signaling.
A single bit or bit sequence may be used for precoding confirmation and may be sufficient for some applications. The use of advanced signaling such as precoding validation using confirmation significantly reduces the signaling overhead. Therefore error checking and detection is desirable.